Rhizobial Strains Research Articles

Symbiotic Effectiveness of Acid Tolerant Nodulating Rhizobia on Growth, Yield and Nutrient Uptake of Pigeon pea (Cajanus cajan L.) in Acidic Alfisols

The symbiotic association between root nodulating bacteria viz. Rhizobium and pulses enhance the crop agronomic characteristics, productivity and quality depending upon the symbiotic effectiveness of the bacterial strain. To evaluate this effectiveness, a study was conducted during December, 2019−April, 2020 (rabi) at Central Farm of Odisha University of Agriculture and Technology, Bhubaneswar- 751003, Odisha aimed at evaluating the efficiency of seven isolated rhizobial strains of pigeon pea viz. BRP-2, BRP-4, BRP-8, BRP-20, BRP-28, BRP-56 and a local strain CHRS-7 in a randomized block design with four replications. The pigeon pea cv PRG-176 was used for study. The results revealed that seed inoculation with different Rhizobium strains enhanced the plant height (41.84–90.09 cm), relative growth rate (0.410−0.898 mm day-1), nodular characteristics, nodular nitrogen (3.11 to 4.11%), pod and seed characteristics in pigeon pea. In addition to that the potentiality of pigeon pea producing only 408 kg seed ha-1 without any seed inoculation could be enhanced to produce 888 kg seed ha-1 by seed inoculation in a coastal agroecosystem. The findings also revealed a better uptake of nutrients by the crop in Rhizobium inoculated practices that performed in the order Control <BRP-20<BRP-8<BRP-4<BRP-56<BRP-28<BRP-2<CHRS-7. The performance of local isolated rhizobial strain (CHRS-7) was better over other strains and it gives cardinal importance for the enhancement of pigeon pea growth, productivity and economics in a coastal acidic Alfisols.

Dependence on Nitrogen Availability and Rhizobial Symbiosis of Different Accessions of Trifolium fragiferum, a Crop Wild Relative Legume Species, as Related to Physiological Traits.

Biological nitrogen fixation by legume-rhizobacterial symbiosis in temperate grasslands is an important source of soil nitrogen. The aim of the present study was to characterize the dependence of different accessions of T. fragiferum, a rare crop wild relative legume species, from their native rhizobia as well as additional nitrogen fertilization in controlled conditions. Asymbiotically cultivated, mineral-fertilized T. fragiferum plants gradually showed signs of nitrogen deficiency, appearing as a decrease in leaf chlorophyll concentration, leaf senescence, and a decrease in growth rate. The addition of nitrogen, and the inoculation with native rhizobia, or both treatments significantly prevented the onset of these symptoms, leading to both increase in plant shoot biomass as well as an increase in tissue concentration of N. The actual degree of each type of response was genotype-specific. Accessions showed a relatively similar degree of dependence on nitrogen (70–95% increase in shoot dry mass) but the increase in shoot dry mass by inoculation with native rhizobia ranged from 27 to 85%. In general, there was no correlation between growth stimulation and an increase in tissue N concentration by the treatments. The addition of N or rhizobial inoculant affected mineral nutrition at the level of both macronutrient and micronutrient concentration in different plant parts. In conclusion, native rhizobial strains associated with geographically isolated accessions of T. fragiferum at the northern range of distribution of the species represent a valuable resource for further studies aimed at the identification of salinity-tolerant N2-fixing bacteria for the needs of sustainable agriculture, as well as in a view of understanding ecosystem functioning at the level of plant-microorganism interactions.

Effect of Rhizobium Inoculation on Growth of Common Bean in Low-Fertility Tropical Soil Amended with Phosphorus and Lime

The cultivation of grain legumes (e.g., common bean) in sub-Saharan Africa contributes to the provision of food for a growing population and delivers environmental benefits such as inputs of nitrogen (N) to crops and soil via symbiotic nitrogen fixation (SNF). However, the success of SNF is constrained by several factors such as the poor efficiency of native rhizobial strains to fix N, the low availability of phosphorus (P) and the acidity of soils. Two trials have been conducted in low-fertility tropical soils at the smallholder farm scale in Madagascar to assess the effects of Rhizobium inoculation together with inputs of P and lime on the growth of the common bean. We showed that inoculation with native strains of Rhizobium had significant effects on bean root nodulation, which was increased by up to 15-fold on plant growth, which increased by 78% and on bean yield, which increased by 126%. Moreover, we observed positive and significant relationships between inoculation with Rhizobium and P fertilization on nodulation, plant growth and yield. However, the addition of dolomite lime did not show any effect in our study. The addition of P decreased the mycorrhization rate of roots. Additional research is still needed to improve our understanding of soil fertility conditions (mainly on nutrient availability, including micronutrients) allowing better efficiency of legume symbionts (rhizobium and mycorrhiza) in such low-fertility soils.

Effects of Rhizobia Isolated from Coffee Fields in the High Jungle Peruvian Region, Tested on Phaseolus vulgaris L. var. Red Kidney.

Soils in the high jungle region of Peru continuously face erosion due to heavy rain, which leads to significant nutrient losses. Leguminous plants may provide a sustainable solution to this problem due to their ability to fix atmospheric nitrogen with the help of symbiotic rhizospheric microbes that reside in their root nodules and help restore soil fertility. The aim of this study was to isolate native rhizobial strains that can form functional nodules in red kidney beans to help improve their growth, development, and yield in field conditions. Rhizobium strains were isolated from soil samples collected from coffee fields using bean plants as trap hosts. The strain RZC12 was selected because it showed good root nodule promotion and a number of PGPR (plant-growth-promoting rhizobacteria) attributes. In the field, bean plants inoculated with the strain RZC12 and co-cultivated with coffee plants produced approximately 21 nodules per plant, whereas control plants produced an average of 1 nodule each. The inoculation with RZC12 significantly increased plant length (72.7%), number of leaves (58.8%), fresh shoot weight (85.5%), dry shoot weight (78%), fresh root weight (85.7%), and dry root weight (82.5%), compared with the control. The dry pod weight produced by the plants inoculated with RZC12 was 3.8 g, whereas the control plants produced 2.36 g of pods. In conclusion, RZC12 is a promising strain that can be used in field conditions to improve the overall productivity of red kidney beans.

Beneficial effect of Rhizobium laguerreae co-inoculated with native Bacillus sp. and Enterobacter aerogenes on lentil growth under drought stress

A collection of 29 Rhizobium laguerreae strains phylogenetically different originating from 4 biogeographic regions of Morocco were tested for their PGP activities and phenotypic traits. The strains showed different levels of tolerance to salt ranging from 0.5 to 1.5% NaCl, an optimal growth in neutral pH (7) and were sensitive to low (10 °C) and high (40 °C) temperatures. Sixteen strains showed important IAA production (50–123 μg IAA/ml) and 11 were identified as high phosphate solubilizers (greater than 20 μg/ml). A pot experiment enabled the selection of 3 R. laguerreae strains LMR575, LMR597, and LMR655 with a symbiotic efficiency of 78, 78 and 76% respectively. In a subsequent greenhouse experiment, the elite rhizobial strains were tested in single and combined inoculations with 2 PGP strains Bacillus sp. LMR698 and Enterobacter aerogenes LMR696 previously isolated from lentil rhizosphere using field soil. All treatments underwent two irrigation levels (30 and 50% of water retention capacity). Under sufficient watering conditions (50%), the combination of R. laguerreae LMR655 with both bacterial strains (E. aerogenes LMR696 and Bacillus sp. LMR698 increased plants biomass by 38 and 23% respectively and number of nodules (54 and 52 nodules/plant respectively). Whereas, under drought stress conditions (30%), all combination except R. laguerreae LMR575+ Bacillus sp. LMR698 yielded a shoot dry weight significantly comparable to nitrogen-fertilized control. Moreover, R. laguerreae LMR597 and LMR655 combined with E. aerogenes showed an increase of areal biomass of 8 and 3% respectively. These performing strains could be further exploited in agricultural practices to mitigate the drought stress effects for a sustainable lentil cultivation.

The Genome of the Acid Soil-Adapted Strain Rhizobium favelukesii OR191 Encodes Determinants for Effective Symbiotic Interaction With Both an Inverted Repeat Lacking Clade and a Phaseoloid Legume Host.

Although Medicago sativa forms highly effective symbioses with the comparatively acid-sensitive genus Ensifer, its introduction into acid soils appears to have selected for symbiotic interactions with acid-tolerant R. favelukesii strains. Rhizobium favelukesii has the unusual ability of being able to nodulate and fix nitrogen, albeit sub-optimally, not only with M. sativa but also with the promiscuous host Phaseolus vulgaris. Here we describe the genome of R. favelukesii OR191 and genomic features important for the symbiotic interaction with both of these hosts. The OR191 draft genome contained acid adaptation loci, including the highly acid-inducible lpiA/acvB operon and olsC, required for production of lysine- and ornithine-containing membrane lipids, respectively. The olsC gene was also present in other acid-tolerant Rhizobium strains but absent from the more acid-sensitive Ensifer microsymbionts. The OR191 symbiotic genes were in general more closely related to those found in Medicago microsymbionts. OR191 contained the nodA, nodEF, nodHPQ, and nodL genes for synthesis of polyunsaturated, sulfated and acetylated Nod factors that are important for symbiosis with Medicago, but contained a truncated nodG, which may decrease nodulation efficiency with M. sativa. OR191 contained an E. meliloti type BacA, which has been shown to specifically protect Ensifer microsymbionts from Medicago nodule-specific cysteine-rich peptides. The nitrogen fixation genes nifQWZS were present in OR191 and P. vulgaris microsymbionts but absent from E. meliloti-Medicago microsymbionts. The ability of OR191 to nodulate and fix nitrogen symbiotically with P. vulgaris indicates that this host has less stringent requirements for nodulation than M. sativa but may need rhizobial strains that possess nifQWZS for N2-fixation to occur. OR191 possessed the exo genes required for the biosynthesis of succinoglycan, which is required for the Ensifer-Medicago symbiosis. However, 1H-NMR spectra revealed that, in the conditions tested, OR191 exopolysaccharide did not contain a succinyl substituent but instead contained a 3-hydroxybutyrate moiety, which may affect its symbiotic performance with Medicago hosts. These findings provide a foundation for the genetic basis of nodulation requirements and symbiotic effectiveness with different hosts.

High throughput pH bioassay demonstrates pH adaptation of Rhizobium strains isolated from the nodules of Trifolium subterraneum and T. repens

The purpose of developing this high throughput assay was to determine whether there was evidence of pH adaptation in strains of rhizobia which nodulate subterranean clover (SC) and white clover (WC), and whether this was related to the pH of the soil of origin. pH is a first-order factor influencing the niche preferences of soil microorganisms and has been convincingly shown to be a key driver of soil bacterial communities. Naturalised strains of Rhizobium spp. that are pH-adapted may have the potential to better compete and/or persist in acidic or alkaline soils compared with introduced commercial strains. Three pilot studies were conducted to design the optimised bioassay. This bioassay tested the effect of pH-amended yeast mannitol broth (seven pH values from pH 4.5–9.0), across three time points, on the in vitro growth of 299 Rhizobium strains isolated from the nodules of SC and WC. The media pH where strains demonstrated fastest growth was related to the pH of the soil that strains were isolated from. However, the correlation between media pH and soil pH was strongly influenced by the growth of strains from alkaline soils (alkaline adaptation), especially in strains isolated from SC nodules.

Carbon metabolic adjustment in soybean nodules in response to phosphate limitation: A metabolite perspective

The necessity to gain deep insights regarding the overall metabolic efficiency of soybean functional acclimation to tackle phosphate (Pi) starvation has led us to discuss the current knowledge on the carbon (C) metabolic changes in soybean nodules under such Pi stress conditions in this review. Soybean possesses numerous coping strategies to conserve Pi utilization, while decreasing the C cost to promote nodule function during Pi stress. This could be achieved through the modulation of carbohydrate importation, mobilization of storage reserves, modification of respiratory pathways and exportation of nitrogenous (N) products. Under such circumstances, soybean regulates the C partitioning among the various nutrient-acquiring structures and the C flux through different metabolic pathways (primary and secondary). However, substantial genetic variation leading to nodule acclimation to Pi stress is notable and dependent on the crop genotypes and/or rhizobial strains that are in symbiosis. Several Pi deficiency-induced responses (e.g., mycorrhizal association, exudative burst and secondary metabolism) can act to increase the Pi levels in nodules, which are, unavoidably, often associated with a heavy burden to the overall C budget of the host. Alternative non-adenylate respiratory pathways (e.g., glycolytic bypass) and ureide export (i.e., less amide transport) are metabolically less expensive, and thus more favorable during Pi stress. • Pi starvation affects carbon (C) metabolic activities in soybean nodules. • Soybean possesses numerous coping strategies to optimize nodular C cost. • Rhizobial microsymbionts markedly affect the Pi deficiency-induced C expenditure. • C acclimation to Pi stress involves primary and secondary metabolic pathways. • Non-adenylate respiratory pathways and ureide export are metabolically less expensive.

Evaluation of Bacillus and Rhizobium Strains to Enhance the Growth of Vigna radiata (L.) under Drought Stress

In the present study, strains of Bacillus and Rhizobium were evaluated for their efficacy to produce auxin and to enhance the growth of Vigna radiata (L.) under drought stress. Colorimetric analysis indicated the production of auxin in bacterial culture supernatants in the presence of 0, 200, and 500 µg ml-1 L-tryptophan. At 500 µg ml-1 of L-tryptophan, B. subtilis Z-24, and B. simplex Z-38 produced significant levels of 41.4 and 24.8 µg ml-1 auxin, respectively. High Performance Liquid Chromatography (HPLC) also detected the auxin production by bacterial strains. In vitro rooting assay also recorded maximum increase in number of lateral roots with B. simplex Z-02, over control. For pot trials, seeds treated with single and mixed bacterial cultures were grown under 28%, 20%, and 10% field capacities (FC) of loamy soils. At 28% FC (normal water level), maximum increase of 28% dry weight was observed for R. rosettiformans Z-30; as compared to respective control. At 10% FC (highest water stress), significant increases of 87% and 70% in fresh weight and root length were recorded by B. cereus Z-59 and B. simplex Z-37, respectively. In case of mixed culture, C-3 (Z-38, Z-20, and Z- 30) and C-2 (Z-59, Z-20, and Z-23) were the most effective to enhance up to 68% dry weight and 13% shoot length of plants under drought stress (10% FC). Results showed that Bacillus and Rhizobium strains have the potential to produce auxin and improved the growth of mung beans under drought stressed conditions.

Iron effect on symbiotic efficiency of horse gram

Four horse gram Rhizobium (HGR) strains HGR-4, 6, 13 and 25 grown under different concentrations of Iron (Fe) were inoculated individually to horse gram plants. These plant sets were screened for their net photosynthetic rate (PN), pod formation and symbiotic efficiency. Horse gram plants inoculated with the strain HGR-4 have shown high PN values at 100 µg g-1 of Fe. The number of pods formed were maximum upon inoculation with HGR-4 at 300 µg g-1 of Fe. Nodulation was maximum with the prior inoculation of the strains HGR-6, 13 and 25 at 500 µg g-1 of Fe. Leghaemoglobin content was maximum on inoculation with HGR-6, 13 and 25 at 300 µg g-1 of Fe. This study demonstrated that the horse gram plants associated with rhizobia, besides having nitrogen fixing capacity also have shown Fe stress tolerance and the ability to remove Fe from soils. Hence, the study confirms the ability of HGR-4, HGR-6, HGR-13 and HGR-25 isolates of Rhizobium to have tolerance of the metal Fe at the plant nodule during pot experiments. Therefore these isolates could be suggested for cultivation of horse gram plants in Fe contaminated soils. These findings imply that horse gram-rhizobia symbiosis is an essential element of plant adaptation to metal stress. Key words: Iron, rhizobia, metal tolerance, symbiotic efficiency

Identification of conserved and new miRNAs that affect nodulation and strain selectivity in the Phaseolus vulgaris-Rhizobium etli symbiosis through differential analysis of host small RNAs.

Phaseolus vulgaris plants from the Mesoamerican centre of genetic diversification establish a preferential and more efficient root nodule symbiosis with sympatric Rhizobium etli strains. This is mediated by changes in host gene expression, which might occur either at the transcriptional or at the post-transcriptional level. However, the implication of small RNA (sRNA)-mediated control of gene expression in strain selectivity has remained elusive. sRNA sequencing was used to identify host microRNAs (miRNAs) differentially regulated in roots at an early stage of the symbiotic interaction, which were further characterized by applying a reverse genetic approach. In silico analysis identified known and new miRNAs that accumulated to a greater extent in the preferential and more efficient interaction. One of them, designated as Pvu-miR5924, participates in the mechanisms that determine the selection of R. etli strains that will colonize the nodules. In addition, the functional analysis of Pvu-miR390b verified that this miRNA is a negative modulator of nodule formation and bacterial infection. This study not only extended the list of miRNAs identified in P. vulgaris but also enabled the identification of miRNAs that play relevant functions in nodule formation, rhizobial infection and the selection of the rhizobial strains that will occupy the nodule.

ISOLATION AND CHARACTERIZATION OF RHIZOBIUM FROM LEGUMES AND ITS ASSOCIATION WITH PLASMIDS

In an attempt to check the direct involvement of plasmid in nodulation and nitrogen fixation, rhizobia were isolated from two legumes; Arachis hypogea (groundnut), Phaseolus vulgaris (beans) and from the soil as control. They were purified and subjected to various morphological, cultural, biochemical analysis and antibiotics test. All the strains showed resistance to most of the antibiotics but exhibited high resistance against Ciprofloxacin and Ofloxacin. The isolates were then subjected to plasmid DNA isolation and their molecular sizes were determined in gel electrophoresis using standard molecular marker. In addition, plates of rhizobial strains treated with UV radiation and plate without UV treatment were independently used to inoculate a sterilized soil where the beans and groundnut were planted followed by appropriate controls. The results showed that rhizobium natural environment is very necessary for proper nodulation and also that plasmid has a role to play in the process of nodulation

Nodulation competitiveness and diversification of symbiosis genes in common beans from the American centers of domestication

Phaseolus vulgaris (common bean), having a proposed Mexican origin within the Americas, comprises three centers of diversification: Mesoamerica, the southern Andes, and the Amotape-Huancabamba Depression in Peru-Ecuador. Rhizobium etli is the predominant rhizobium found symbiotically associated with beans in the Americasalthough closely related Rhizobium phylotypes have also been detected. To investigate if symbiosis between bean varieties and rhizobia evolved affinity, firstly nodulation competitiveness was studied after inoculation with a mixture of sympatric and allopatric rhizobial strains isolated from the respective geographical regions. Rhizobia strains harboring nodC types α and upgamma, which were found predominant in Mexico and Ecuador, were comparable in nodule occupancy at 50% of each in beans from the Mesoamerican and Andean gene pools, but it is one of those two nodC types which clearly predominated in Ecuadorian-Peruvian beans as well as in Andean beans nodC type upgamma predominated the sympatric nodC type δ. The results indicated that those beans from Ecuador-Peru and Andean region, respectively exhibited no affinity for nodulation by the sympatric rhizobial lineages that were found to be predominant in bean nodules formed in those respective areas. Unlike the strains isolated from Ecuador, Rhizobium etli isolated from Mexico as well from the southern Andes was highly competitive for nodulation in beans from Ecuador-Peru, and quite similarly competitive in Mesoamerican and Andean beans. Finally, five gene products associated with symbiosis were examined to analyze variations that could be correlated with nodulation competitiveness. A small GTPase RabA2, transcriptional factors NIN and ASTRAY, and nodulation factor receptors NFR1 and NFR5- indicated high conservation but NIN, NFR1 and NFR5 of beans representative of the Ecuador-Peru genetic pool clustered separated from the Mesoamerican and Andean showing diversification and possible different interaction. These results indicated that both host and bacterial genetics are important for mutual affinity, and that symbiosis is another trait of legumes that could be sensitive to evolutionary influences and local adaptation.

CHARACTERIZATION AND COMPARATIVE RESPONSE OF RHIZOBIA ISOLATES FROM ROOT NOODLES OF SELECTED WEED SPECIES AND SOYBEAN (Glycine max) TO ENVIRONMENTAL FACTORS

Screening and selecting the most effective strains of rhizobium is important for biological nitrogen fixation. To determine the effects of environmental factors on rhizobia strains associated with some selected leguminous weed species, rhizobia strains isolated from root nodules of five weed species (Mimosa pudica, Crotolaria retusa, Desmodium triflorum, Canavalina ensiformis, Stylosanthes spp.) were subjected to varying temperature, salinity, and pH in the laboratory. Results indicated better growths at temperatures of 30 and 370C compared to the temperature of 250C. Results further showed that microbial growth was optimal at 1.5% salt concentration. Optimum growth was also obtained at the pH range of 5 and 8. The study further revealed by a series of morphological and biochemical tests that all the strains were gram-negative, rod-shaped, and mucous producing. Rhizobia strains from leguminous weeds were found to exhibit faster growth than the strain nodulating soybean in all the conditions to which they were subjected. A cross inoculation study was therefore recommended to access the compatibility of these rhizobial strains from the wild with cultivated leguminous plant species.

Benefits of silicon-enhanced root nodulation in a model legume are contingent upon rhizobial efficacy

AimsSilicon (Si) uptake and accumulation improves plant resilience to environmental stresses, but most studies examining this functional role of Si have focussed on grasses (Poaceae) and neglected other important plant groups, such as legumes (Fabaceae). Legumes have evolved a symbiotic relationship with nitrogen-fixing bacteria (rhizobia) housed in root nodules. Our study determined the impacts of silicon (Si) supplementation on Medicago truncatula inoculated with Ensifer meliloti rhizobial strains that differed in their capacity for nitrogen fixation: Sm1021 (‘low-efficiency’) or Sm1022 (‘high-efficiency’).MethodsWe examined how Si and rhizobial efficacy influence nodule and plant functional traits, including their chemical aspects. These combinations were supplied with or without Si in a glasshouse experiment, where we quantified nodule flavonoids and foliar chemistry (free amino acids, soluble protein, elemental C, N and Si).ResultsSi supply increased nodule number per plant, specific nodule flavonoid concentrations, contents of foliar nitrogenous compounds and foliar C, but not foliar Si. We also demonstrated that rhizobial efficacy altered the magnitude of Si effects on certain traits. For example, Si significantly promoted concentrations of foliar N and soluble protein in the plants associated with the ‘low-efficiency’ strain only, and this was not the case with the ‘high-efficiency’ one.ConclusionsCollectively, our study indicates that Si generates positive effects on M. truncatula, particularly when the association with rhizobia is relatively inefficient, and may play a more prominent role in rhizobial functionality than previously thought.

Rhizobium croatiense sp. nov. and Rhizobium redzepovicii sp. nov., two new species isolated from nodules of Phaseolus vulgaris in Croatia

Phaseolus vulgaris is a legume indigenous to America which is nodulated by strains of genus Rhizobium in Croatia. Four of these strains, 13TT, 9T, 18TT and 8Z are phylogenetically close to the species from the Rhizobium leguminosarum phylogenetic complex in the 16S rRNA gene analysis. The results of both the analyses of the concatenated recA and atpD genes and whole genomes revealed that the strains 13TT and 9T clustered with Rhizobium sophoriradicis CCBAU 03470T and the strains 18TT and 8Z with Rhizobium ecuadorense CNPSO 671T. Whole genome average nucleotide identity blast (ANIb) and dDDH values between the strains 13TT and the type strain of R. sophoriradicis and between the strains 18TT and the type strain of R. ecuadorense were lower than 95% and 70%, respectively, which are the threshold values recommended for bacterial species differentiation. These results combined with those of chemotaxonomic and phenotypic analyses support the affiliation of these strains to two novel species within the genus Rhizobium for which we propose the names Rhizobium croatiense sp. nov. 13TT (=LMG 32397T, = HAMBI 3740T) as type strain and Rhizobium redzepovicii sp. nov. 18TT (=LMG 32398T, = HAMBI 3741T) as type strain.

The Cell Membrane of a Novel Rhizobium phaseoli Strain Is the Crucial Target for Aluminium Toxicity and Tolerance.

Soils with low pH and high aluminium (Al) contamination restrict common bean production, mainly due to adverse effects on rhizobia. We isolated a novel rhizobium strain, B3, from Kenyan soil which is more tolerant to Al stress than the widely used commercial strain CIAT899. B3 was resistant to 50 µM Al and recovered from 100 µM Al stress, while CIAT899 did not. Calcein labeling showed that less Al binds to the B3 membranes and less ATP and mScarlet-1 protein, a cytoplasmic marker, leaked out of B3 than CIAT899 cells in Al-containing media. Expression profiles showed that the primary targets of Al are genes involved in membrane biogenesis, metal ions binding and transport, carbohydrate, and amino acid metabolism and transport. The identified differentially expressed genes suggested that the intracellular γ-aminobutyric acid (GABA), glutathione (GSH), and amino acid levels, as well as the amount of the extracellular exopolysaccharide (EPS), might change during Al stress. Altered EPS levels could also influence biofilm formation. Therefore, these parameters were investigated in more detail. The GABA levels, extracellular EPS production, and biofilm formation increased, while GSH and amino acid level decreased. In conclusion, our comparative analysis identified genes that respond to Al stress in R. phaseoli. It appears that a large portion of the identified genes code for proteins stabilizing the plasma membrane. These genes might be helpful for future studies investigating the molecular basis of Al tolerance and the characterization of candidate rhizobial isolates that perform better in Al-contaminated soils than commercial strains.

Screening and increase of exopolysaccharide production by rhizobial strains, stress tolerances and its efficiency with "in Vivo" peanut plants

Screening and increase of exopolysaccharide production by rhizobial strains, stress tolerances and its efficiency with "in Vivo" peanut plants

Impact of Two Strains of Rhizobium leguminosarum on the Adaptation to Terminal Water Deficit of Two Cultivars Vicia faba.

Drought stress has become one of the most uncontrolled and unpredictable constraints on crop production. The purpose of this study was to evaluate the impacts of two different Rhizobium leguminosarum strains on terminal drought tolerance induction in two faba bean genotypes cultivated in Algeria, Aquadulce and Maltais. To this end, we measured physiological parameters—osmoprotectants accumulation, oxidative stress markers and enzyme activities—to assess the effect of R. leguminosarum inoculation on V. faba under terminal water deficiency conditions in greenhouse trials. Upregulation of anti-oxidative mechanisms and production of compatible solutes were found differentially activated according to Rhizobium strain. Drought stress resilience of the Maltais variety was improved using the local Rhizobium strain OL13 compared to the common strain 3841. Symbiosis with OL13 strain leads in particular to a much better production of proline and soluble sugar in nodules but also in roots and leaves of Maltais plant. Even if additional work is still necessary to decipher the mechanism by which a Rhizobium strain can affect the accumulation of osmoprotectants or cellular redox status in all the plants, inoculation with selected Rhizobium could be a promising strategy for improving water stress management in the forthcoming era of climate change.

Efficiency of using new Rhizobium strains on legume crops

During significant time, the use of bean-rhizobial systems and development of effective, competitive microbial preparations have been an integral part of organic farming. Also, in intensive technologies, only due to such ones, it is possible without reducing the achieved level of agricultural production to reduce its cost, harmful effects on the environment and at the same time to achieve ecological purity of products selection of highly effective strains that have adapted to local soil and climatic conditions and acquired resistance to nutrients and plant protection is the most promising strategy to increase the effectiveness of microbial inoculants. The aim of this work was to select highly effective strains that have adapted to local soil and climatic conditions and have become resistant to nutrients and plant protection and are the most promising for improving the effectiveness of microbial inoculants. Field researches were conducted in the research fields of the Skvyra Research Station of Organic Production of the Institute of Agroecology and Environmental Management of NAAS (Ukraine, Kyiv region, Skvyra) during 2020–2021. Nitrogen-fixing activity of root nodules was determined by acetylene method. The gas mixture was analyzed on an «Agilent 6850 chromatograph». The paper presents the results of research to establish the effectiveness of new strains of inoculants on crops of legumes: soybean of Moravia variety and peas of Starter variety in the Kyiv region, Skvyra Research Station of Organic Production of the Institute of Agroecology and Environmental Management of NAAS. The significant effect of new rhizobia strains for inoculation of legumes on phenological indicators and yield of these crops in the conditions of intensive technologies was shown. The competitiveness of strains is controlled by both internal determinants — genotype of the microorganism, and external factors such as symbiont plant physiology, exposure to abiotic factors, tolerance to pesticides and agrochemicals used in crop production technologies. It has been shown that the use for inoculation of soybean strain B. japonicum EL 35 and for inoculation of peas strain R. leguminosarum bv. viciae PS 12 stimulate the development of plants during their growing season and allow to obtain symbiotic systems with a high level of nitrogen fixation, as a result of which we can increase the yield of legumes from 16 to 20%.